fix: add Send bound to Streaming wrapper

[infiniteregrets]

useful for moving ownership to the spawn closure,

let mut response_stream = client.append_session(request).await?;

    let response_consumer = tokio::spawn(async move {
        while let Some(n) = response_stream.next().await {
            if let Err(e) = n {
                error!(?e, "receiver error")
            }
        }
    });